1. Field of the Invention
This invention relates to the field of wind energy production. More specifically the invention comprises a partially self-erecting wind turbine tower which significantly reduces the lift height required for assembly of the components.
2. Description of the Related Art
FIG. 1 depicts a prior art wind turbine 10. Pylon 14—which may include two or more joined segments—is affixed via base 24 to foundation 12. Nacelle 16 houses a revolving horizontal shaft to which hub 18 and blades 20 are attached. The nacelle typically also contains a gearbox for stepping up the rotational speed of hub 18, a generator for converting the rotating shaft energy to electrical energy, control electronics, and a braking mechanism (which may be mechanical, electrical, or a combination of the two).
Nacelle 16 is attached to the top of pylon 14 via yaw joint 22. Drive mechanisms revolve the nacelle with respect to pylon 14 in order to point hub 18 into the wind. FIG. 1 depicts a prior art device in which the rotating blades are located upwind of the pylon, which is true for most wind turbines currently in production. There are many variations on this design. There are also prior art wind turbines in which the rotating blades are located downwind of the pylon. The present invention may be adapted for use with many different types of prior art turbines.
The use of a single pylon in the prior art requires the diameter “D” of foundation 12 to be quite large. The mass of the foundation is required to counteract the large overturning forces placed on the base. The foundation is generally cast from concrete, and the use of such a large structure adds to the overall cost of the wind turbine installation.
The components of a prior art wind turbines are typically installed using a crane. FIG. 2 shows crane 26 lifting nacelle 16 onto the top of the pylon. Boom 28 holds a cable to which hook 30 is attached. The height of the unitary pylon and nacelle will determine the “hook height.” “Hook height” is a term of art in the rigging industry. It simply means the height above the ground for the engagement portion of a lifting hook. Boom 28 must of course extend above the hook height in order to allow some vertical space for the cable and pulley assemblies. The reader will thereby easily discern that the required hook height determines the size of crane needed for a particular wind turbine installation.
Prior art wind turbines are quite large. Blade lengths vary between 20 meters (66 feet) and 60 meters (197 feet). The largest wind turbines have overall heights of about 200 meters (656 feet with overall blade diameters of 125 meters (400 feet). A very large wind turbine will have a pylon height of about 100 meters (328 feet). Thus, a crane having a hook height of about 120 meters (394 feet) is needed to install the largest examples of prior art wind turbines. Such wind turbines are typically installed in remote locations, where access for large machinery is limited. Transporting extremely large cranes to such sites represents a substantial portion of the total cost of installing a wind turbine. Thus, a wind turbine tower design that could be erected using a smaller crane would be advantageous.